Method of making diacyl peroxides



United States Patent 3,397,245 METHOD OF MAKING DIACYL PEROXIDES HerbertR. Appell, Pitcairn, Pa., assignor to Koppers Company, Inc, acorporation of Delaware No Drawing. Continuation-impart of applicationSer. No. 251,023, Jan. 14, 1963. This application June 17, 1966, Ser.No. 558,231

11 Claims. (Cl. 260-610) This invention relates to the preparation ofdiacyl peroxides. In one specific aspect it relates to a catalyticprocess for the preparation of symmetrical and unsymmetrical diacylperoxides. This application is a continuation-inpart of my co-pendingapplication Ser. No. 251,023, filed Jan. 14, 1963, now abandoned.

Diacyl peroxides have many uses in industry. For example, benzoylperoxide is widely used as a free radical catalyst in the polymerizationof styrene and other monomers; it is also used in bleaching flour andfood oils. Acetyl benzoyl peroxide is useful in the polymerization ofacrylics and unsaturated esters and also finds use as a chemicalintermediate. Some peroxides which decompose readily, e.g., a'cetylperoxide, are used in polymerization processes operating at moderatetemperatures and other peroxides having greater stability, e.g.p-chlorobenzoyl peroxide, are used at higher temperatures. In general,the peroxides prepared according to the present invention are useful ina temperature range of from room temperature up to about 125 C.Ordinarily, the less stable peroxides are used at temperatures near thelower limits of this range. However, in the presence of activators eventhe more stable peroxides may be used at, or below, room temperature.

The term diacyl peroxides as used herein is synonymous witha,a'-diOXOp6IOXid6S and is intended to include diacyl peroxides, diaroylperoxides, and acyl-aroyl peroxides.

Heretofore, symmetrical diacyl peroxides, that is, those in which the Rgroups in the equations below are the same, have been prepared by thereaction of an excess of acid anhydride or acyl chloride with alkalinesolutions of hydrogen peroxide as illustrated by the equations.

I ll 2(RCO);O N840: Rd-O-O-OR ZNaOCOR III 0 o o Unsymrnetrical diacylperoxides have not been produced commercially because of the diflicultyof preparing these peroxides by previously known methods.

It is therefore an object of the present invention to provide a novelprocess for preparing diacyl peroxides.

It is another object of this invention to provide a process forpreparing a wide variety of unsymmetrical diacyl peroxides.

In accordance with the present invention, I have discovered a method ofmaking diacyl peroxides which comprises reacting preferably underanhydrous conditions, at a temperature of 0-75 C. an organic acidanhydride of the formula (-RCO) O wherein -R is a member selected fromthe group consisting of lower alkyl, phenyl, lower alkyl phenyl,halophenyl, nitrophenyl and naphthyl, and an aldehyde of the formula llRCH 3,397,245 Patented Aug. 13, 1968 "ice wherein R is a member selectedfrom the group consisting of lower alkyl, phenyl, lower alkyl phenyl,halophenyl, and naphthyl with oxygen in the presence of a catalyst ofthe formula i RC-OM wherein M is a metal selected from the groupconsisting of magnesium and lithium, R is as defined aforesaid, and a isan integer having a value corresponding to the valence of said metal.

This reaction is illustrated by the equation:

IV 0 O 0 II II wherein R and R are defined as aforesaid. The diacylperoxide is symmetrical when R is the same as R and unsymmetrical when Ris dilferent from R'.

Acid anhydrides useful in the reaction have the general formula (RCO) Owherein R is lower alkyl, phenyl, lower alkyl phenyl, halophenyl,nitrophenyl and naphthyl. Representative compounds include aceticanhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride,toluic anhydride, t-butylbenzoic anhydride, chlorobenzoic anhydride,nitrobenzoic anhydride, naphthoic anhydride, etc. Although the bestyields in the aliphatic series are obtained with straight chainanhydrides, especially with the lower members in the series, branchedchain anhydrides, such as isobutyric anhydride, can be used if lowerperoxide yields are acceptable. Relatively inert anhydrides such asphthalic anhydride and tetrachlorophthalic anhydride are not useful inthis invention.

In general, aldehydes which can be autoxidized to form compoundscontaining active oxygen can be used in this invention. Aldehydes usefulin the reaction have the general formula wherein R is lower alkyl,phenyl, lower alkyl phenyl, halophenyl, and naphthyl. Representativealdehydes include acetaldehyde, propionaldehyde, n-butyraldehyde,isobutyraldehyde, benzaldehyde, tolualdehyde, chlorobenzaldehydes,naphthaldehydes, etc. However, aldehydes such as nitrobenzaldehydes,terephthaldehyde and phthaldehydic acid have little or no utility inthis invention.

T-he catalysts useful in this reaction are the magnesium and lithiumsalts of organic acids. The organic acids from which such lithium ormagnesium salts are made should have a dissociation constant (Ka)greater than 1 l0- Organic acids having a dissociation constant of lessthan l 10- are too sluggish to give suitable yield of the peroxides. Theorganic acids should also form salts which are soluble in the reactionmedium.

The acids which have been found to be best suited are the fatty acidshaving up to eight carbon atoms and chlorinated derivatives thereof, andbenzoic acid with its halogenated, nitrated and lower alkylatedderivatives. Examples of such fatty acids are acetic, propionic acid,butyric acid, hexanoic acid, chloracetic acid, etc. Examples of thebenzoic acids useable are; benzoic acid, chlorobenzoic acid,bromobenzoic acid, nitrobenzoic acid, toluic acid, ethyl benzoic and thelike.

Preferably, lithium and magnesium salts of such organic acids are usedwhich are soluble in the reaction medium, and although insoluble saltsmay be used, these were found to be less effective. It is also preferredthat the salt of the organic acid corresponding to the acid anhydride beused to enable ready separation of the prodcomponent, lithium ormagnesium acetate is preferably used as the catalyst; similarly ifbenzoic anhydride is the anhydride component, lithium or magnesiumbenzoate is preferably used as catalyst. It is not essential to use thesalt of the corresponding anhydride but purification of the peroxide issimplified because of the absence of foreign anions.

A convenient method of preparing the catalysts consists of dissolvingthe magnesium or lithium carbonate in the appropriate organic acid. Whenthe acid anhydride contains some of the parent acid, the catalyst may beformed in situ by merely adding the magnesium or lithium carbonate tothe impure acid anhydride. Other methods of preparing the salts oforganic acids will be obvious to those skilled in the art.

The quantities of catalysts normally used between range 0.01 and 1percent. Less than the minimum amount results in decreased yieldswhereas more than the maximum amount shows no improved effectiveness.

The temperatures required for preparing the products of the novelreaction range from C. to about 75 C. Most diacyl peroxides areconveniently prepared in the 20-50 C. range. Generally, the less stablediacyl peroxides are prepared at the lower temperatures and the morestable peroxides at the higher temperatures.

The manufacturer of diacyl peroxides using the catalysts of thisinvention may be conducted batchwise or continuously. Certain peroxidesare more adaptable to a batch process and others to a continuousprocess. Benzoyl peroxide, e.g., is readily obtained by continuouslyremoving a stream of crude product from the reactor filtering the crudebenzoyl peroxide, and recycling the filtrate to the reactor.

Ultraviolet radiation, ozone, or salts of cobalt, copper, manganese,etc. may also be used in combination with the catalysts of thisinvention, but they are not required and best results are ordinarilyobtained in their absence.

Inert'solvents may be used when the starting materials or products arenormally solid. Useful solvents include ketones such as acetone andacetophenone; organic acids such as acetic, propionic, butyric, andbenzoic acid; oxidation resistant alcohols, such as t-butyl alcohol; andnormally liquid paraffins and cycloparaflins, such as hexane andcyclohexane. In particular, acetone may be used when the oxygen ispressured into a closed reaction system. However, when air or oxygen ispassed through a reactor, a high boiling solvent, such as acetophenone,is preferred to minimize losses due to volatilization. Organic acidwhich may be used must correspond to the anhydride being reacted e.g.acetic acid is used as solvent for a reaction involving aceticanhydride.

The stoichiometry of the reaction requires that the molar ratio ofanhydride to aldehyde be one to one. In many instances, an excess ofanhydride to aldehyde is preferred. More specifically, the less reactiveanhydrides give better results when present in a molar excess over thealdehyde.

My invention is further illustrated by the following examples.

EXAMPLE I Benzaldehyde (15 ml.), benzoic anhydride (37 gms.), lithiumbenzoate (0.8 gm.) and 40 ml. acetophenone were placed in a liter flaskfitted with a stirrer and a gas dispersion tube. The flask was placed ina water bath at 42-43 C. and stirring and oxygen fiow started. Every twohours the solution was removed, cooled to about 16 C. and theprecipitate of benzoyl peroxide and benzoic acid collected. Makeupbeuzaldehyde and benzoic anhydride were added to the filtrate and theresulting liquid returned to the autoxidation reactor. After five cyclesthe yield of recovered benzoyl peroxide was between 95 and 98 percentand the rate of reaction had not diminished.

4 EXAMPLE II Benzaldehyde (10 gms.), propionic anhydride (13 gms.), andpropionic acid (2 gms.) were placed in the autoxidation reactor with .04percent by weight of lithium carbonate. After 1.5 hours at 45 C. a 92percent yield of propionylbenzoyl peroxide was obtained. The peroxide,an oily liquid, was isolated by pouring into cold water and. washingwith 10 percent sodium carbonate solution.

EXAMPLE III A series of experiments was conducted to determine therelative eifectiveness of various catalysts. Five grams of benzaldehyde,10 grams of benzoic anhydride and 10 grams of acetone were placed ineach of four identical pyrex autoxidation reactors. The catalyst, amountof catalyst. and the conversion to benzoyl peroxide after two hours ofautoxidation at 40 C. is shown in Table I.

TABLE I Reactor Catalyst Amount, Conversion to percent Benzoyl peroxide1 Lithium Benzoate 0.02 52 2- .do 0. 2 70 Magnesium Benzoate 0.2 74 4Magnesium Carbonate. 0. 2 21 EXAMPLE IV o-Chlorobenzaldehyde (12.5),acetic anhydride (10 gms.), acetic acid (2 ml.) and lithium acetate(0.04 gm.) were placed in the autoxidation reactor and treated with astream of oxygen at 40 C. for two hours. A 90 percent conversion toacetyl o-chlorobenzoyl peroxide was isolated by pouring the product intocold water and collecting the solid peroxide.

EXAMPLE V Lithium carbonate (0.1 gram) was dissolved in 20 ml. n-butyricanhydride containing 10 percent butyric acid. This solution was added to10 gms. benzaldehyde and autoxidized in a stream of oxygen at 40 C.After two hours an percent conversion to n-butyryl benzoyl peroxide wasachieved. The peroxide was isolated by pouring into cold water andseparating the liquid peroxide layer.

EXAMPLE VI To a one liter glass flask, fitted with a porous glass inletin the bottom, were added 106 gr. of benzaldehyde, 112 gr. of aceticanhydride, 11 gr. of acetic acid and 2 gr. of lithium benzoate. Theflask was held at 35 C. (water bath) with stirring while oxygen was fedthrough the glass inlet. After ca 1 hour titration indicated thereaction was complete. The crude product was poured into cold water, thecrystals formed separated by filtration, washed with water and dried.Acetyl benzoyl peroxide in 89% yield was obtained.

EXAMPLE VII To an autoxidation reactor there was added 30 gr. ofbenzaldehyde, 74 gr. of benzoic anhydride and 1.5 gr. of magnesiumacetate. The reaction mixture was treated with an oxygen stream for twohours at 40 C. The mixture was then poured into 5% aqueous sodiumcarbonate solution and the precipitated product separated by filtration.The conversion to benzoyl peroxide was EXAMPLE VIII ing mto ice waterand separating the organic layer. This peroxide was not stable at roomtemperture and required storage at C.

EXAMPLE IX Following the procedure of Example II and using theanhydride, solvent, and catalyst set forth therein, p-tolualdehyde andl-naphthaldehyde were substituted for the aldehyde component.Satisfactory yields were obtained.

EXAMPLE X Following the procedure of Example H and using the samealdehyde and catalyst set forth therein, acetone was substituted as thesolvent and m-toluic anhydride, p-nitrobenzoic anhydride,o-chlorobenzoic anhydride, and 2- naphthoic anhydride were substitutedfor the anhydride component. Satisfactory yields were obtained.

I claim:

1. A method of making diacyl peroxides comprising reacting at atemperature of 0-75 C.

(a) an organic acid anhydride of the formula (RCO) O wherein R is amember selected from the group consisting of lower alkyl, phenyl, loweralkyl phenyl, halophenyl, nitrophenyl and naphthyl and (b) an aldehydeof the formula 0 RCH wherein R' is a member selected from the groupconsisting of lower alkyl, phenyl, lower alkyl phenyl, halophenyl, andnaphthyl with (c) oxygen in the presence of a catalyst comprising ametal salt of a carboxylic acid, said metal being selected from thegroup consisting of lithium and magnesium, said salt being soluble inthe reaction mixture.

2. The method of claim 1 wherein said carboxylic acid is an aliphaticacid having up to eight carbon atoms.

3. The method of claim 1 wherein said carboxylic acid is selected fromthe group consisting of benzoic acid, halogenated benzoic acids,nitrated benzoic acids and lower alkylated benzoic acids.

4. A method of making diacyl peroxides comprising reacting at atemperature of 0-75 C.

(a) an organic acid anhydride of the formula (RCO) 0 wherein R is amember selected from the group consisting of lower alkyl, phenyl, loweralkyl phenyl, halophenyl, nitrophenyl and naphthyl and 6 (b) an aldehydeof the formula R'dH wherein R is a member selected from the groupconsisting of lower alkyl, phenyl, lower alkyl phenyl, halophenyl, andnaphthyl with (c) oxygen in the presence of (d) a catalyst of theformula wherein M is a metal selected from the group consisting oflithium and magnesium, R is defined as aforesaid, and a is an integerhaving a value corresponding to the valence of said metal.

5. The method according to claim 4 wherein R is the same as R.

6. The method according to claim 4 wherein R is different from R.

7. The method of claim 4 wherein the diacyl peroxide is acetylbenzoylperoxide, the organic acid anhydride is acetic anhydride, the aldehdyeis benzaldehyde and the catalyst is lithium acetate.

8. A method of making acetyl-benzoyl peroxide comprising reacting at atemperature of 0-75 C. benzoic anhydride and acetaldehyde with oxygen inthe presence of a catalytic amount of magnesium benzoate.

9. A method of making benzoyl peroxide comprising reacting at atemperature of 075 C. benzoic anhydride and benzaldehyde with oxygen inthe presence of a catalytic amount of lithium benzoate.

10. A method of making benzoyl peroxide comprising reacting at atemperature of 0-75 C. benzoic anhydride and benzaldehyde with oxygen inthe presence of a catalytic amount of magnesium benzoate.

11. The method of claim 4 wherein the diacyl peroxide is acetylperoxide, the temperature is 0-25 C., and the organic acid anhydride isacetic anhydride, the aldehdye is acetaldehyde and the catalyst ismagnesium acetate.

No references cited.

BERNARD HELFIN, Primary Examiner.

W. B. LONE, Assistant Examiner.

1. A METHOD OF MAKING DIACYL PEROXIDES COMPRISING REACTING AT A TEMPERTURE OF 0-75*C. (A) AN ORGANIC ACID ANHYDRIDE OF THE FORMULA (RCO)2O WHEREIN R IS A MEMBER SELECTED FROM THE GROUP CONSISTING OF LOWER ALKYL, PHENYL, LOWER ALKYL PHENYL, HALOPHENYL, NITROPHENYL AND NAPHTHYL AND (B) AN ALDEHYDE OF THE FORMULA 